The overall goals of the proposed research are: (a) to obtain a clearer understanding of the structural implications of the sliding filament hypothesis as related to tension development at various sarcomere lengths; (b) to consider the role of the nervous system in, and the cytoarchitectural basis (at the electron microscopic level) for, different rates of contraction in developing muscle fibers with known histochemical characteristics; (c) to study degenerative changes in nerve and muscle resulting from tourniquet ischemia; (d) to consider the structural and cytochemical basis of dedifferentiation or degeneration of the contractile apparatus in muscle disease.